1. Technical Field of the Invention
This invention is related generally to position determination, and more particularly to position determination using broadcast radio signals.
2. Description of Related Art
It is often desirable, and sometimes necessary, for a person to know their current location. If the person has a cell phone, conventional wireless communications networks currently provide a number of different techniques for positioning the cell phone within the wireless network. One technique uses the cell identity combined with either the Round Trip Time (RTT), Timing Advance (TA) or measured signal strength to determine an area within the cell that the mobile terminal is located. Another technique uses signals from multiple neighboring base stations to calculate the mobile terminal's location based on the Time Difference of Arrival (TDOA), Angle of Arrival (AOA) or received signal strength of the signals. Still another technique used in code division multiple access (CDMA) networks uses signal timing to position the mobile terminal in the CDMA network.
However, if the person does not have a cell phone or is an area that does not provide cellular service, there are only limited options to obtain the person's location. One option is the well-known Global Positioning System (GPS). However, the GPS method requires adequate reception from a minimum of four satellites to accurately determine the spatial position of an object in three dimensions. Obtaining an adequate signal from four satellites is often difficult depending on the terrain and physical environment. For example, large obstructions, thick tree cover, tall buildings, canyons, underground tunnels and other obstacles may cause a satellite to become obscured and thus preclude an accurate GPS position.
Therefore, a need exists for an alternative positioning method when traditional cellular and GPS techniques are not available.